The present invention relates to a sensor for analyzing gases.
Sensors used to analyze the exhaust gas of internal combustion engines are described in Automotive Electronics Handbook (1994), Chapter 6, Wiedenmann et al., xe2x80x9cExhaust Gas Sensorsxe2x80x9d. However, with these sensors, the problem of overswings or counterswings taking place when a jump response is carried out following a gas change procedure occurs during operation, particularly at high oxygen pump loads. These overswings or counterswings are known as xcex=1 ripple.
A gas sensor according to the present invention has an advantage in that the xcex=1 ripple, i.e., the counterswings or overswings that may occur with a jump response to gas change procedures, is reduced so that the sensor signal can be generated more quickly and precisely and is subject to fewer fluctuations.
At least in the hot area of the sensor, the measuring electrode supply conductor and/or the inner pump electrode supply conductor are in contact with an oxygen reservoir that makes a sufficient quantity of oxygen available at all times; this prevents an oxygen shortage at an electrode supply conductor when the pump voltage is applied during operation of the sensor, which tends to cause a Nernst voltage with respect to the other electrode supply conductors due to the resulting concentration difference, which, in turn, significantly contributes to the xcex=1 ripple.
To ensure the actual measuring area with which the inner pump electrode and the measuring electrode are in contact is not enlarged by the oxygen reservoir according to the present invention in an undesirable manner, this reservoir and the measuring area are separated by a gas-tight barrier in an advantageous manner.
Furthermore, instead of or in addition to the measuring electrode supply conductor and/or the inner electrode supply conductor being in contact with an oxygen reservoir, it is advantageous if the outer electrode supply conductor is in contact with an oxygen reservoir. This means oxygen shortages and the resulting disruptive Nernst voltages at the outer electrode supply conductor can be avoided.
In contrast, in the case of sensors known from the related art, foil binders (ZrO2) or other foils that have been applied via a printing process, for example, form a gas-tight seal around the electrode supply conductors of the measuring electrode, the inner electrode and the outer electrode within the vitrified sensor element; as a result, any oxygen shortage cannot be offset.
It should be noted that a person skilled in the art would understand the xe2x80x9chotxe2x80x9d area of the sensor to mean the area of the gas sensor which is exposed to the gas to be measured and in which, respectively, the measuring signal is generated; one would understand the xe2x80x9ccoldxe2x80x9d area to mean the area of the electrode supply conductors that is exposed to much lower temperatures and makes little contribution to generating the measuring signal.
It is advantageous to use a hollow space which is in contact with the inner pump electrode supply conductor and/or the outer pump electrode supply conductor and/or the measuring electrode supply conductor as the oxygen reservoir. Herein, it is advantageous if the inner pump electrode supply conductor and the outer pump electrode supply conductor are both in contact with one, possibly the same, hollow space or oxygen reservoir.
Furthermore, it is advantageous if the outer electrode supply conductor is in contact with an oxygen reservoir, in some areas this supply conductor not being covered by the usual cover layer, so that the outer electrode supply conductor is in direct contact there with the ambient air or another oxygen-containing gas.
It is advantageous if the gas-tight barrier separating the measuring area from the oxygen reservoir is a barrier, in particular, a barrier that is composed of a ZrO2 foil binder.
Instead of or in addition to a hollow space, it is advantageous if the oxygen reservoir takes the form of a porous material or is provided as a layer that is porous in at least some areas. To accomplish this, it is advantageous if the porous material is in at least some areas in contact with the measuring electrode supply conductor and/or the inner pump electrode supply conductor and/or the outer pump electrode supply conductor, in the form of one or a plurality of porous areas. It is advantageous if the porous area is part of a solid electrolyte foil that maintains separation between the electrode supply conductors. It is advantageous to use porous ZrO2 or Al2O3 as the porous material for the porous area.
Furthermore, it is advantageous if the oxygen reservoir is in contact with at least one electrode supply conductor not only in some areas of the hot area of the sensor, but also in the cold area of the sensor.